Technical area

The present invention relates to a control unit and a method to control a vehicle in a vehicle platoon. The vehicle platoon comprises at least one lead vehicle and one additional vehicle, each of which has a positioning unit and a unit for wireless communication.

Background to the invention

The intensity of traffic is high on major roads in Europe, and it is expected to increase. The increased transport of people and goods not only gives rise to traffic problems in the form of traffic queues, it also requires ever-increasing amounts of energy, which eventually gives rise to the emission of, for example, greenhouse gases. One possible contribution to solving these problems is to allow vehicles to be driven closer together in what are known as "vehicle platoons". The term

"vehicle platoon" is here used to denote a number of vehicles with short distances between them, being driven as a single unit. The short distances lead to it being possible for more traffic to use the road, and the energy consumption for an individual vehicle will be reduced since the drag is reduced. The vehicles in the vehicle platoon are driven with at least one of an automated control of the speed of the vehicle and an automated control of its direction. This leads to vehicle drivers such as truck drivers being subject to a reduced load, accidents based on erroneous human decisions being reduced, and the possibility of reducing fuel consumption. Studies show that the fuel consumption of the leading vehicle in the vehicle platoon can be reduced by 2 to 10%, and that of the following vehicle by 15 to 20%, from the fuel consumption of a vehicle driving alone. This is the case in conditions in which the distance between the vehicles is 8-16 metres and the speed at which they travel is 80 km/h. The reduced fuel consumption gives a corresponding reduction in the emission of CO2.

Drivers are already using this well-known fact, which has a reduced traffic safety as a consequence. One fundamental question related to vehicle platoons is how the time gap between vehicles can be reduced from the recommended 3 seconds to a value between 0.5 and 1 second, without affecting traffic safety. With distance sensors and cameras, the reaction time of the driver can be eliminated. This is a type of technology that is already being used today by systems such as ACC (adaptive cruise control) and LKA (lane-keeping assistance). Adaptive cruise-control is based on measuring using sensors the instantaneous speed and distance only to vehicles in front (or to neighbouring vehicles) and maintaining a desired distance.

Distance sensors and cameras, however, require a clear view of the target, and this makes it difficult to detect events that are more than one vehicle ahead in the queue. A further limitation is that the cruise-control system cannot act proactively, i.e., it cannot react to events that occur further in advance in the traffic that are going to affect the traffic rhythm.

One possibility to enable vehicles to act proactively is to arrange that the vehicles communicate in order to be able to exchange information between them. One development of the IEEE-standard 802.1 1 for WLAN (wireless local area networks) known as "802.1 1 p" makes possible the wireless transfer of information between vehicles, and between vehicles and infrastructure. Different types of information, such as vehicle parameters and strategies, can be transmitted to and from the vehicles.

The development of communication technology, thus, has made it possible to design vehicles and infrastructure that can interact and act proactively. Vehicles can act as a unit and thus a shorter distance between them, and better global traffic flow, is made possible.

WO-2012105889-A1 mentions that it is possible to take into consideration obstacles such as traffic lights, speed limits, etc., that lie ahead along the road in order to avoid, for example, unnecessary braking when the obstacle is

discovered. When a vehicle drives in a vehicle platoon with short distances between each other, the vehicle is affected to a large degree by how the vehicle immediately in front of it in the vehicle platoon behaves. It is thus an object to provide a method to control a vehicle in a vehicle platoon in a fuel-efficient manner. Summary of the invention

According to a first aspect, the object described above is at least partially achieved through a method to control a vehicle f _k in a vehicle platoon that comprises at least one lead vehicle and one additional vehicle, each of which has a positioning unit and a unit for wireless communication. The method comprises receiving at least one vehicle parameter φ that describes a property of the vehicle f _k -i that lies immediately in front of the vehicle f^ determine data β about the surroundings, which data describe a property of the surroundings of the vehicles; predicting a behaviour for the vehicle f _k -i in front, based on the vehicle parameter φ that describes a property of the vehicle f _k -i and the data β about the

surroundings, and determining a driving strategy for the vehicle f _k based on the predicted behaviour of the vehicle f _k -i in front, after which the vehicle f _k is controlled according to the driving strategy.

A fuel-efficient and safe regulation is achieved through the method since the vehicle f _k can be controlled according to the predicted behaviour of the vehicle f _k -i in front. Consideration can be taken of the capacity of the vehicle in front, whether it has poorly functioning brakes, etc. The distance between the vehicles can be controlled according to the predicted behaviour of the vehicle f _k _i , such that safety is not compromised.

Since information is given about future events that can affect the vehicle f _k , the vehicle f _k can plan its driving in a better manner such that the regulation of the vehicle f _k becomes smooth and safe. The method does not depend on having complete information and data about the complete vehicle platoon, and in this way the calculation complexity is reduced, and the possibility that the regulation can be carried out in practice increases. According to a second aspect, the object described above is at least partially achieved through a control unit to control a vehicle f _k in a vehicle platoon that comprises at least one lead vehicle and one additional vehicle, each of which has a positioning unit and a unit for wireless communication. The control unit is configured to: receive at least one vehicle parameter φ that describes a property of the vehicle f _k -i that lies immediately in front of the vehicle f _k in the vehicle platoon; determine data β about the surroundings, which data describe a property of the surroundings of the vehicles; predict a behaviour for the vehicle f _k -i in front, based on the vehicle parameter φ that describes a property of the vehicle f _k -i and the data β about the surroundings; determine a driving strategy for the vehicle f _k based on the predicted behaviour of the vehicle f _k -i in front; generate a driving strategy signal that indicates the driving strategy; and control the vehicle f _k according to the driving strategy. According to a third aspect, the object is at least partially achieved through a computer program P at a system, where the said computer program P comprises program code in order to cause the system to carry out any one of the method steps that are described in this application. According to a fourth aspect, the object is at least partially achieved through a computer program product comprising a program code stored on a medium that can be read by a computer in order to carry out any one of the method steps described in this application. Preferred embodiments are described in the non-independent claims and in the detailed description.

Brief description of the attached drawings

The invention will be described below with reference to the attached drawings, of which:

Figure 1 illustrates a vehicle platoon that is travelling up a hill.

Figure 2 shows an example of a vehicle in the vehicle platoon. Figure 3 illustrates a control unit according to one embodiment.

Figure 4 shows a flow diagram for a method according to one embodiment.

Detailed description of preferred embodiments of the invention

Definitions

LAC (look-ahead cruise control): a cruise-control system that uses information about the topography of the road ahead, and calculates an optimal driving profile in the form of a speed trajectory for a vehicle. Also known as a "predictive cruise- control system".

LAP (look-ahead cruise control for platoons): a cooperative cruise-control system that uses information about the topography of the road ahead, and calculates an optimal driving trajectory for all vehicles in a vehicle platoon. Also known as a "predictive cruise-control system for vehicle platoons". The regulatory strategy is determined by, for example, dynamic programming.

v _k : the speed of the vehicle f _k in the vehicle platoon with N vehicles.

dk,k+i - the distance between vehicle fk and the vehicle behind it f _k+ i in the vehicle platoon.

<¾: the gradient at vehicle f _k .

V2V-communication (vehicle-to-vehicle): wireless communication between vehicles, also known as vehicle-to-vehicle communication.

V2l-communication (vehicle-to-infrastructure): wireless communication between vehicles and infrastructure, such as road junctions and computer systems.

Figure 1 shows a vehicle platoon with N heavy vehicles f _k that is driving up a hill with small spaces d _k , _k +i between the vehicles. The vehicles in the vehicle platoon are driven with at least one of an automated control of the speed and an automated control of its direction. The gradient at vehicle f _k when it drives up the hill is shown as <¾. Each vehicle f _k is equipped with a receiver and a transmitter for wireless signals, partially shown with an antenna. The vehicles f _k in the vehicle platoon can thus communicate with each other through V2V-communication or through other means such as, for example, mobile communication units, through an application in a communication unit, or through a server. They can

communicate also with infrastructure in the form of V2l-communication. The communication can pass, for example, from one vehicle through a road junction to a second vehicle. The different vehicles fk have different masses m _k . The vehicle platoon has a lead vehicle, i.e. the first vehicle fi . Each vehicle fk in the vehicle platoon has, for example, a unique vehicle identity and a vehicle platoon identity that is common for the complete vehicle platoon, in order to be able to maintain knowledge of which vehicles are members of the vehicle platoon. Data that are transmitted wirelessly between the vehicles in the vehicle platoon can be tagged with these identities such that the vehicle of origin of the data received can be determined. Figure 2 shows an example of a vehicle fk in the vehicle platoon, here the lead vehicle fi , and illustrates how it may be equipped. The vehicle fk is equipped with a positioning unit 5 that can determine the position of the vehicle fk. The

positioning unit 5 may be, for example, configured to receive signals from a global positioning system such as GNSS (Global Navigation Satellite System), for example GPS (Global Positioning System), GLONASS, Galileo or Compass.

Alternatively, the positioning unit 5 may be configured to receive signals from, for example, one or several detectors in the vehicle that measure relative distances to, for example, a road junction, vehicles in the surroundings, or similar entities, with known positions. Based on the relative distances, the positioning unit 5 can subsequently determine the position of the vehicle fk. A detector may be configured also to detect a signature in, for example, a road junction, whereby the signature represents a certain position. The positioning unit 5 may in this case be configured to determine its position through detection of the signature. The positioning unit 5 may instead be configured to determine the signal strength of one or several signals from a base station or road junction with known position, and in this way to determine the position of the vehicle fk by triangulation. The position of the vehicle fk can in this way be determined. Of course, the technologies described above may be combined in order to determine the position of the vehicle fk. The positioning unit 5 is configured to generate a positioning signal that contains the position p of the vehicle fk, and to transmit this signal to one or several units in the vehicle fk. The vehicle fk is, as has been mentioned above, equipped also with a unit 4 for wireless communication. The unit 4 is configured to function as receiver and transmitter of wireless signals. The unit 4 can receive at least one of wireless signals from other vehicles and wireless signals from infrastructure around the vehicle fk, and it can transmit at least one of wireless signals to other vehicles and wireless signals to infrastructure around the vehicle fk. The wireless signals can comprise vehicle parameters from other vehicles, such as their mass, torque developed, speed, braking power, and also more complex information such as, for example, the currently used driving profile, driving strategy, etc. The wireless signals may contain also information about the surroundings, such as the gradient a of the road, the radius of curvature r, etc. The vehicle fk may be equipped also with one or several detectors 7 in order to detect the surroundings, for example a radar unit, a laser unit, a gradient gauge, acceleration gauge, steering wheel measure, a gyro, etc. These detectors are generally labelled in Figure 2 as a detector unit 7, but they may be constituted by several different detectors located at different locations in the vehicle fk. The detector unit 7 is configured to determine a parameter, such as a relative distance, speed, gradient, lateral acceleration, rotation, steering wheel measure, etc., and to generate a detector signal that contains the parameter. The detector unit 7 is further configured to transmit the detector signal to one or several units in the vehicle fk. The vehicle fk may be equipped also with a road horizon unit 6 that comprises map data 8 (Figure 3) about the road ahead. The road horizon unit 6 is configured to generate a road horizon h that describes the road ahead of the vehicle fk. The road horizon h comprises properties such as, for example, the gradient and radius of curvature at positions along the horizon. The vehicle fk communicates internally between its various units through, for example, a bus, such as a CAN bus (controller area network), which uses a message-based protocol. Examples of other communication protocols that can be used are TTP (time-triggered protocol), Flexray, etc. Signals and data as described above can in this way be exchanged between various units in the vehicle fk. Signals and data can instead be transferred in a wireless manner, for example, between the various units.

Also a control unit 1 may be arranged in the vehicle fk, which is illustrated in Figure 2. The control unit 1 can communicate with the other units 4, 5, 6 and 7 as has been explained previously, and can receive data from them. Alternatively, the control unit 1 may be placed in an external unit, and communicate with and receive data from the second units 4, 5, 6 and through wireless communication. Also the road horizon unit 6 may be placed in an external unit. The task of the control unit 1 is to predict how the vehicle f _k -i in front of the vehicle fk in the vehicle platoon is going to behave at the road ahead, and to adapt the regulation of the vehicle f _k -i in a fuel-optimal manner based of the predicted behaviour of the vehicle fk.

An example of the control unit 1 is shown in Figure 3. The control unit 1 may be, for example, an ECU (electronic control unit). The control unit 1 comprises a processor unit 2 and a memory unit 3 that comprise a computer program P. The computer program P comprises programme code to cause the control unit 1 to carry out any one of the method steps that will be described below, with reference to the flow diagram in Figure 4 and the control unit 1 in Figure 3. The other units 4, 5, 6, 7 can comprise one or several processor units and one or several memory units. A processor unit may be constituted by a CPU (central processing unit). The memory unit may comprise a transient or a non-transient memory or it may comprise a transient and a non-transient memory, such as flash memory or RAM (random access memory). Also an existing cruise-control system 9 is shown in Figure 3, to which cruise-control system a driving strategy signal can be transmitted, as will be explained in more detail below.

The method comprises receiving at least one vehicle parameter φ that describes a property of the vehicle f _k -i that lies immediately in front of the vehicle fk in the vehicle platoon (A1 ). This vehicle parameter φ may describe, for example, any one of the mass, engine power, brake power, frontal area, a property of the propulsion or a property of the gearbox of the vehicle f _k -i . The vehicle parameter φ may, for example, be transmitted by V2V from the vehicle f _k -i in front to the control unit 1 through the unit 4 for wireless communication in the vehicle f _k or through a server, road junction, mobile communication unit or an application in a

communication unit. The method comprises also to determine data β about the surroundings, which data describe a property of the surroundings of the vehicles (A2). The data β about the surroundings may, for example, describe a property of the road ahead of the vehicles, such as its gradient, degree of curvature or speed limit. This information can be obtained by detecting the gradient or degree of curvature of the road with an appropriate detector 7. The information can be obtained also through wireless communication from another vehicle or from infrastructure such as, for example, a road junction or a computer system. A speed-limit sign can, for example, specify its speed limit by wireless

communication that can be transmitted to the vehicle f _k . Information about obstacles ahead such as, for example, another vehicle ahead on the road, a traffic jam, etc., can be transmitted through V2V or V2I to the vehicle f _k . According to one embodiment, the control unit 1 is given access to a road horizon h from the road horizon unit 6. The road horizon h comprises properties of the road ahead, and thus it contains data β about the surroundings. The data β about the surroundings may comprise also one or several scenarios for the road ahead, thus different gradients, radii of curvature, etc. The method comprises further to predict a behaviour for the vehicle f _k -i in front, based on the vehicle parameter φ that describes a property of the vehicle f _k -i and the data β about the surroundings (A3). The prediction may be based also on several vehicle parameters φ or a combination of vehicle parameters φ. The behaviour of the vehicle f _k _i in front may be predicted based on, for example, a model of the vehicle f _k _i . A model that describes the principal forces that act on the vehicle f _k _i can be described according to: m

dt F 'broms ^luftmotstand (^ ^ruUning (.^ Fgravitet ^

= T(w _e , 5) - F _brake - - c _D A _a p _a v ² - c _r mg cos - mg sin , (1 )

where a describes the gradient of the road, c _D and c _r are characteristic coefficients, g describes the force of gravity, p _a is the air density, r _w is the wheel radius, and i _t , i _f , ¾, r\ _f are constants specific for the transmission and gearing. The accelerating mass of the vehicle m _t (m,J _w ,J _e , i _t , i _f , r\ _t , r\ _f ) depends on the gross mass m, wheel inertia J _w , engine inertia J _e , , the gear ratio and efficiency of the gearbox i _t , % and the final gear ratio and efficiency i _f , r\ _f . Predicting a behaviour for the vehicle f _k -i comprises, according to one embodiment, to determine the speed v _k- i of the vehicle f _k -i along the road ahead. Since the road ahead is known through the horizon unit 6 (Figure 3) and a vehicle model of the vehicle f _k -i is available, the predicted speed v _k- i for the vehicle f _k -i along the road horizon h can be determined, given a preset speed for the vehicle f _k _i that this vehicle is to maintain. The preset speed is normally the same for all vehicles in the vehicle platoon, and is available in the vehicle fk. The predicted speed can be determined based on a local LAC strategy, or based on a common LAP strategy. For example, the speed of the vehicle f _k _i can be calculated based on minimising the fuel consumption and minimising the time required for a driving session. An optimisation can then be carried out based on the vehicle model according to Equation (1 ). The method comprises further to determine a driving strategy for the vehicle fk based on the predicted behaviour of the vehicle f _k _i in front (A4). The driving strategy for the vehicle fk can be determined, for example, such that the vehicle fk principally holds a predetermined distance to the vehicle f _k _i in front. This driving strategy can be determined, for example, through suitable optimisation algorithms, such as, for example, dynamic programming. The control unit 1 can be configured also to receive a previous driving strategy for the vehicle fk through, for example, V2V or V2I, and to adapt this previous driving strategy according to the behaviour of the vehicle f _k -i in order to create a particular driving strategy. The control unit 1 (Figure 3) is configured to generate a driving strategy that indicates the driving strategy that has been determined. The vehicle fk is thereafter controlled according to the driving strategy (A5). The driving strategy may contain, for example, a driving profile with speed reference values v _re f at various positions along the road ahead. The driving strategy can be transmitted to an existing cruise-control system 9 (Figure 3) that controls the accelerator and brake of the vehicle fk such that the vehicle fk obtains essentially the speed v _re f.

The behaviour of the vehicle f _k -i may be, for example, that it will achieve a slightly lower speed than the preset speed in an uphill section due to the fact that it does not have sufficient vehicle power in order to cope with the uphill section. The vehicle fk behind can then plan its driving and can determine a driving strategy such that it is to reduce the pressure on the accelerator at a certain position or time along the road, such that it also achieves the same lower speed as that obtained by vehicle f _k -i in the uphill section. The vehicle fk does not then need to brake in the uphill section in order to be able to maintain a predetermined distance between the vehicles. The control unit 1 can determine also how the vehicle fk is affected by the various forces according to Equation (1 ), and can calculate the speed or speeds that the vehicle fk should be controlled to at various positions or times in order to achieve the predicted speed of the vehicle f _k -i according to its predicted behaviour. According to a further example, the control unit 1 can determine at least one of the distance between the vehicles fk and f _k _i and the speed of the vehicle fk, according to predetermined regulations for various vehicle parameters φ. In the case in which φ specifies, for example, a certain brake power, etc., for the vehicle f _k- i , the control unit 1 may determine, for example, that a certain distance between the vehicles fk and f _k _i is to be maintained in order to ensure safety. The present invention is not linnited to the embodiments described above. Various alternatives, modifications and equivalents can be used. For this reason, the embodiments named above do not limit the scope of the invention, which is defined by the attached claims.